Capacitor



L. J. SPERRY 3,328,865

July 4, 1967 CAPACITOR Original Filed March 6, 1963 INVENTOR. LEONARD J.SPERRY ATTORNEY ugugl United States Patent 3,328,865 CAPACITOR LeonardJ. Sperry, Milwaukee, Wis., assignor to Globe- Union Inc., Milwaukee,Wis., a corporation of Delaware Original application Mar. 6, 1963, Ser.No. 263,255, now Patent No. 3,258,665, dated June 28, 1966. Divided andthis application Jan. 5, 1966, Ser. No. 518,903

11 Claims. (Cl. 29-2542) This application is a division of co-pendingapplication Ser. No. 263,255, filed Mar. 6, 1963, now Patent No.3,258,665, and assigned to the assignee of this application.

This invention relates to variable capacitors and, more particularly, toan improved capacitor rotor and its method of construction.

It is well recognized that capacitance varies inversely with thedistance between the capacitor plates and this characteristic wouldappear to lend itself quite Well to providing high capacitance valueswithout an increase in size of the unit. In variable capacitors,particularly those wherein the capacitor rotor provides the dielectricmedium as well as the means by which the capacitor plates are moved intoand out of alignment, the mechanical strength of the rotor is anotherfactor for consideration in that a minimum rotor thickness must bemaintained in order to withstand handling during both assembly andoperation without excessive rotor breakage. This is a universal problemin the design of variable capacitors of this type but is particularlyacute in the area of miniaturized capacitor units. For these reasons,the physical or mechanical characteristics of the capacitor rotor haverestricted rotor design from an electrical standpoint so that theavailable capacitance range of units constructed in accordance withheretofore accepted procedures has been limited.

An object of this invention is to increase the capacitance range of avariable capacitor.

Another object of this invention is to increase the capacitance range ofa variable capacitor while providing a generally stronger unit andwithout an increase in the size of the unit.

For the achievement of these and other objects, it is proposed toreinforce the rotor of a variable capacitor to permit a reduction in therotor thickness thereby increasing the available over-all capacitancerange.

Other objects and advantages will be pointed out in, or be apparent fromthe description and claims, as will obvious modifications of theembodiment shown in the drawings, in which:

FIG. 1 is a front elevation of one embodiment;

FIG. 2 is a rear elevation thereof;

FIG. 3 is a section along lines 33 of FIG. 1;

FIG. 4 is a front elevation with the rotor removed;

FIG. 5 is an example of an alternative capacitor construction;

FIG. 6 is a front elevation of a rotor construction suitable for use inthe embodiment of FIG. 5;

FIG. 7 is an end view of the rotor of FIG. 6;

v FIG. 8 illustrates another rotor construction suitable for use in theembodiment of FIG. 5; and

FIG. 9 is a section along lines 9-9 of FIG. 8.

It will be appreciated that this invention has universal applicabilityto variable capacitors of all types; however, it is particularly wellsuited for use in miniaturized vari able capacitors wherein thecapacitor rotor also provides the dielectric medium for the capacitorunit and therefore it will be discussed in, but is not limited to, thatenvironment.

With particular reference to the drawing, capacitor 10 .includes a base12 and a rotor 16. A stator plate 14 (see FIG. 4) is provided on base 12by metallizing in any 3,328,865 Patented July 4, 1967 suitable mannerwell known in the art. The configuration of the stator plate can vary asdesired but preferably is semi-circular.

Rotor 16 is connected for rotation with a shaft 18 which extends throughbase 12. One end of shaft 18 is provided with a rolled edge 21 whichengages Y-shaped spring terminal 20 through washer 22. The opposite endof the shaft includes an elongated portion 23 connected to the rotor tocomplete the assembly of the shaft and rotor in the capacitor. Anelectrical terminal 24 is formed integrally with and extends from springterminal 20 for connection to a suitable electrical lead and one of thelegs 25 of spring terminal 20 is positioned between ribs 3030 on base 12so as to hold the spring terminal stationary during movement of rotor16.

A rotor plate 32 is provided on rotor 16 and has a configurationconforming to that of the stator plate. Similarly to stator plate 14,the rotor plate comprises a metallized paint pattern. Movement of rotor16 by turning shaft 18 operates to move the rotor and stator plates intoand out of alignment. To facilitate rotation of the shaft and rotor,elongated portion 23 is generally slotted so as to be capable ofreceiving a suitable adjusting tool.

Stator electrode 14 includes a metallized extension 34 which iselectrically connected to electrical terminal 38 through pin 36. Solder40, 40, between elongated portion 23 and plate 32, both establishes amechanical connection between the shaft and rotor and completes anelectrical circuit to the rotor plate. Accordingly, an electricalcircuit is completed from terminal 24 through spring terminal 20, washer22, shaft 18, and solder connection 40 to the rotor plate. Similarly, anelectrical circuit is completed to the opposite capacitor plate fromterminal 38, through pin 36, metallized extension 34 to the statorplate. Hence the rotor and stator plates become the opposed plates ofthe capacitor with the rotor disposed therebetween to provide thecapacitor dielectric. It will be appreciated that for purposes ofillustration the thickness of the metallized portions has beenexaggerated.

In accordance with this invention, the rotor is reinforced so that itsthickness can be reduced to thereby increase the maximum capacitance anddecrease the minimum capacitance of the unit. It will be observed thatin the embodiment illustrated in FIGS. 1-4 rot-or 16 includes aperipheral ridge 46 and a central hub 44 which form a well 45therebetween. This well is filled with a reinforcing material 48 whichcan be any one of a number of substances such as a glaze or plasticmaterial, either thermosetting or thermoplastic. The reinforcingmaterial is capable of adhering to the rotor and, as it sets or cures,does not strain the rotor. With such reinforcing, approximately 50%reductions in thickness of the rotor, between electrodes, have beenachieved without appreciably reducing rotor strength. For example, in acapacitor unit 10, constructed in accordance with heretofore wellaccepted practices and wherein the combined rotor and base thickness andthe rotor diameter are approximately .297 inch and .640 inchrespectively, the minimum rotor thickness was limited to approximately.019 inch; however, in accordance with this invention it is possible toreduce that rotor thickness to approximately 009-011 inch. Such areduction in thickness decreases the minimum capacity and also increasesthe maximum capacity. More particularly, in the example capacitor givenand with a rotor of suitable ceramic material the available capacitancerange has been increased from approximately 10-1 (5 pf.-50 pf.) toapproximately 22-1 (4 pf.- pf.).

In constructing capacitor 10, the rotor is formed of a suitabledielectric material, such as a ceramic. Conforming metallized patternsare provided on the rotor and base. It should be noted here that themating faces of the rotor and base are optically ground for mostefficient engagement. A reinforcing medium, such as a refractory glazeor suitable plastic, is applied to the surface of the rotor upon whichthe rotor plate is formed. The glaze can be applied in either powder orsolution form and, where it is used, the rotor is subsequently fired tovitrify the glaze. In those instances where a plastic material is usedas the reinforcing medium, it is allowed to cure in a manner and for atime determined by the particular plastic used. The opposite side of therotor, i.e. that opposite to the side on which the reinforcing materialis provided, is ground to reduce the rotor to a desired minimumthickness. The rotor is then assembled onto the base and is ready forconnection in a particular electrical circuit.

In filling well 45 of capacitor 10 care must be taken to control thefill so as not to cover the top of hub 44 or to flow the reinforcingmaterial over ridge 46 as this would cause grinding difficulties as wellas interfere with the provision of a good electrical connection betweenthe solder and the rotor plate.

This invention is applicable to use in other types of variablecapacitors, for example that illustrated in FIG. 5. Capacitor unit 50includes a base 52 and a rot-or 54. Base 52 is provided with ametallized capacitor plate 56 (a portion of plate 56 is shown in FIG. bybreaking away part of rotor 54) having a metallized portion 58 extendingto terminal 60 to which a suitable lead line may be attached.

In addition to the rotor construction discussed above in relation tocapacitor 10, the rotor can be of laminar construction as illustrated inFIGS. 6 and 7. More particularly, rotor 54 includes a reinforcingsegment 64 and a dielectric segment 66 having a capacitor plate 68therebetween. Rotor 54 can be constructed by forming the rotor segments,segment 64 with a notch 70 and segment 66 without a notch, from suitabledielectric material such as a ceramic. Segment 66 is metallized toprovide rotor 68 thereon and segments 64 and 66 are positioned inabutting relationship with plate 68 sandwiched therebetween and withnotch 70 centered on rotor plate 68. The segments are pressed togetherand fired and the outer face 72 of dielectric segment 66 is ground toreduce the thickness of the segment with segment 64 providing thereinforcing necessary to prevent breakage during assembly. Prior toassembly of the rotor in capacitor 50, a metallized paint pattern 74 isscreened onto the outer surface of segment 64 with the paint beingpermitted to flow into notch 70 to electrically contact capacitor plate68. Spring terminal 76 is used to assemble the rotor in the capacitorwith a pin 78 extending through the hase and rotor to complete thecapacitor assembly and provide an axis of rotation for the rotor. Pin 78is electrically connected to a metallized pattern 80, which extends to aterminal 81, and spring terminal 76 electrically engages pattern 74 tocomplete an electrical circuit to plate 68. Accordingly, plates 56 and68 become the opposed plates of the capacitor with segment 66 disposedtherebetween to provide the dielectric.

Preferably metallizing paint is applied to segment 66 and segments 64and 66 are pressed together before the paint is fired. The paint andsegments 64 and 66 are then fired simultaneously to insure a bondedconnection between the segments.

An alternative rotor construction for use in capacitor 50 is illustratedin FIGS. 8 and 9. Rotor 84 includes dielectric segment 86 and a cover orreinforcing segment 88, if desired the dielectric segment can comprise asuitable ceramic and the reinforcing segment can be made of steatite. Inthis construction metallized pattern 90 is provided on segment 86 andpatterns 92 and 94 are provided on both sides of the reinforcingsegment. The segments are joined by a suitable adhesive, such as rubbercement 96, with notch 98 centered on plate 90 and pattern 94 engagingplate 90. The rotor is assembled in the capacitor as described above inrelation to the rotor of FIGS. 6 and 7 and the adhesive cement allowedto cure.

In accordance with this invention presently available capacity rangescan be provided with a reduction in size of the capacitor unit, orgreater capacity ranges can be provided in standard size units.Furthermore, increased capacity ranges can be provided withoutadditional cost and while providing mechanically stronger units.

It is to be understood that the term glaze as used in the specificationand claims designates, as is common in the ceramic art, a coating offired, hard, crystalline refractory material.

Although this invention has been illustrated and described in connectionwith particular embodiments there? of, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit of the invention or from thescope of the appended claims.

What I claim is:

1. The method of manufacturing a variable capacitor element andcomprisingthe steps of forming a dielectric member having oppositelyfacing surfaces,

forming an electrically conductive plate on a portion of one of saiddielectric member surfaces,

and separately applying reinforcing means to said one dielectric membersurface, said reinforcing means being applied in the form of a mediumdistinguishable from said dielectric member and said conductive plate,

said reinforcing means affording structural reinforcing for saiddielectric member and, with the structural support of said reinforcingmeans, providing a predetermined thickness of said dielectric memberbetween said conductive plate and the other of said dielectric membersurfaces which is less than the minimum thickness which said dielectricmember could have from a structural standpoint without said reinforcingmeans.

2. The method of claim 1 wherein said reinforcing means comprises astructurally reinforcing glaze material and including the step of firingsaid glaze material at a predetermined temperature.

3. The method of claim 1 wherein said reinforcing means comprises astructurally reinforcing plastic material and including the step ofcuring said plastic material.

4. The method of manufacturing a rotor for use in a variable capacitorand comprising the steps of forming a dielectric member havingoppositely facing surfaces with one of said surfaces being generallyplanar,

forming an electrically conductive plate on a portion of said onedielectric member surface, providing reinforcing means comprising asecond member having a first generally planar surface, a second surfacefacing oppositely with respect to said first surface and an apertureextending between the oppositely facing surfaces of said second member,

joining said reinforcing means to said dielectric member with saidplanar surfaces of said second member and said dielectric member inopposed relationship with said electrically conductive plate disposedtherebetween and said aperture communicating with said plate,

and preparing the other of said dielectric member surfaces to achieve apredetermined thickness between the oppositely facing surfaces thereofwhich is less than the minimum thickness which said dielectric membercould have from a structural standpoint without said reinforcing means.

'5. The method of claim 4 including the step of forming an electricallyconductive portion on said second surface of said second member andextending through said aperture and contacting the conductive plate onsaid dielectric member.

6. The method of claim 4 wherein said conductive plate is formed of anelectrically conductive paint and said second member and said dielectricmember are pressed together prior to firing said paint and said membersand paint are fired simultaneously,

and wherein electrically conductive portions are formed 7. In the methodof manufacturing a variable capacitor the steps of providing adielectric member having oppositely facing parallel planar surfaces,

forming an electrically conductive plate on a portion of one of saidplanar surfaces,

providing reinforcing means comprising a second memher having agenerally planar surface,

joining said reinforcing means to said dielectric memsaid reinforcingmeans affording structural reinforcing for said dielectric member and,with the support of said reinforcing means providing a capacitor rotorhaving a predetermined thickness of said dielectric member between saidconductive plate and the other of said dielectric member surfaces whichis less than the minimum thickness which said dielectric member couldhave from a structural standpoint without said reinforcing means,

and assembling said rotor with the other of said dielectric membersurfaces in opposed relationship with a second conductive plate.

8. The method of manufacturing a variable capacitor element andcomprising the steps of forming a dielectric member having oppositelyfacing surfaces and with one of said surfaces being generally planar,

forming an electrically conductive plate on a portion of said planarsurface of said dielectric member,

applying reinforcing means to said planar dielectric member surface,said reinforcing means comprising a second member having a generallyplanar face,

joining said dielectric and second members with the planar faces thereofin opposed relationship and with said electrically conductive platedisposed therebetween,

said reinforcing means affording structural reinforcing for saiddielectric member and, with the structural support of said reinforcingmeans, providing a predetermined thickness of said dielectric memberbetween said conductive plate and the other of said dielectric membersurfaces which is less than the minimum thickness which said dielectricmember could have from a structural standpoint without said reinforcingmeans. 9. The method of claim 8 wherein said plate is formed of anelectrically conductive paint and said members are pressed togetherprior to firing said paint and said members and paint are firedsimultaneously.

10. The method of claim 8 including the step of providing an adhesivemedium between and to cooperate in joining said second member anddielectric member.

11. The method of manufacturing a variable capacitor element andcomprising the steps of forming a dielectric member having oppositelyfacing surfaces, forming an electrically conductive plate on a portionof one of said dielectric member surfaces, applying reinforcing means tosaid one dielectric member surface to afford structural reinforcing forsaid dielectric member, and, with said reinforcing means on saiddielectric member to provide structural support, grinding said otherdielectric member surface to achieve a predetermined thickness of saiddielectric member between said conductive plate and the other of saiddielectric member surfaces which is less than the minimum thicknesswhich said dielectric member could have from a structural standpointwithout said reinforcing means.

UNITED I.B.M. Tech. pages 26 and 27.

Burdett 29155.5 Leszynski 29-155.7 X

OTHER REFERENCES Disc. Bull., vol. 3, No. 12, May 1961,

WILLIAM I. BROOKS, Primary Examiner.

1. THE METHOD OF MANUFACTURING A VARIABLE CAPACITOR ELEMENT ANDCOMPRISING THE STEPS OF FORMING A DIELECTRIC MEMBER HAVING OPPOSITELYFACING SURFACES, FORMING AN ELECTRICALLY CONDUCTIVE PLATE ON A PORTIONOF ONE OF SAID DIELECTRIC MEMBER SURFACE, AND SEPARATELY APPLYINGREINFORCING MEANS TO SAID ONE DIELECTRIC MEMBER SURFACE, SAIDREINFORCING MEANS BEING APPLIED IN THE FORM OF A MEDIUM DISTINGUISHABLEFROM SAID DIELECTRIC MEMBER AND SAID CONDUCTIVE PLATE, SAID REINFORCINGMEANS AFFORDING STRUCTURAL REINFORCING FOR SAID DIELECTRIC MEMBER AND,WITH THE STRUCTURAL SUPPORT OF SAID REINFORCING MEANS, PROVIDING APREDETERMINED THICKNESS OF SAID DIELECTRIC MEMBER BETWEEN SAIDCONDUCTIVE PLATE AND THE OTHER OF SAID DIELECTRIC MEMBER SURFACES WHICHIS LESS THAN THE MINIMUM THICKNESS WHICH SAID DIELECTRIC MEMBER COULDHAVE FROM A STRUCTURAL STANDPOINT WITHOUT SAID REINFORCING MEANS.